If you get malaria somewhere in the tropics and end up in a British hospital, the treatment is pretty simple.

Or at least it used to be.

The recommended treatment in the U.K. for "uncomplicated" malaria (that's a case where you're pretty sick but not on death's door) is an artemisinin-based drug combination called Artemether-lumefantrine.

The patient takes a few pills over the course of three or four days, the drugs kill the malaria parasites and everybody feels better. That's why, over the last decade and a half, artemisinin has become the go-to drug to beat back the most common malaria infections both in British hospitals and across much of the developing world.

Recently, however, malaria parasites have started to adapt so the drugs won't knock them out.

Resistance to artemisinin-based medications has been slowly developing in Southeast Asia.

And now these malaria wonder drugs look like they may be starting to lose their mojo in Africa, too.

Late in 2015, health officials in Britain for the first time came across a cluster of malaria cases that refused to succumb to Artemether-lumefantrine. The patients were travelers who had returned from three different African countries — Angola, Liberia and Uganda. After being treated with Artemether-lumefantrine, each patient appeared to be cured.

Then the parasitic infections came racing back.

"It was very surprising," says Dr. Colin Sutherland, from the London School of Hygiene and Tropical Medicine. "We might not get too concerned about the occasional treatment failure.

But when four cases come along at once, it does make us think we've got something important that we need to investigate.

Interestingly at about the same time Swedish colleagues reported a similar finding in Sweden."

In an article published in Antimicrobial Agents and Chemotherapy, Sutherland and his colleagues document the four cases.

Part of what is useful to researchers about these U.K. cases is that the patients were in Britain when their malaria cases rebounded. None of them had left the country after initially being treated.

So when the malaria parasites re-emerged in their systems, the doctors were able to quickly realize that the artemisinin-based drugs had failed.

The patients were subsequently treated with different drugs.

"Because our patients were living in a country where we don't have malaria, we knew it had to be the same parasites that weren't adequately treated the first time around," says Sutherland.

That's not the case in Africa, where people live with malaria on a day-to-day basis. So if they get sick again, he says, "it's difficult to determine if maybe they just got another mosquito bite."

There's been concern about the potential development of artemisinin resistance in Africa but very little concrete evidence that it's happening there.

These cases in the U.K. show that strains of malaria are emerging in Africa that can't be cured with the most common drugs to treat the disease.

But Sutherland urges caution: "It would be unwise for us to sit here in Europe and say, oh, we've got four cases so Africa's got a problem.

But the public health impact in Africa could be enormous. It's a clear message that we need to now put in place the right kind of studies in Africa [to track resistance]."

Malaria remains one of the most troublesome diseases in the developing world. According to the World Health Organization there were more than 200 million cases in 2015 and roughly 430,000 deaths from the disease.

The good news is that efforts against malaria, including insecticide-treated bed nets and artemisinin-based treatments, have cut the rates of malaria transmission particularly in Africa significantly over the last 15 years with the total number of cases in the world dropping by a third and malaria deaths being cut in half.

A treatment for malaria, a life-threatening blood illness caused by parasites transmitted to humans through the bite of the Anopheles mosquito, has failed for the first time according to scientists.

This has promoted fear that the illness could be becoming resistant to primary drugs used to counter it.

The failure of the drug was first noticed in four patients, who were being treated in the UK for an African strain of the mosquito-borne condition.

This led to a team of scientists and medics at the London School of Hygiene and Tropical Medicine (LSH) to investigate whether the drug had become resistant.

The team have said that it maybe "too early to say for sure," but they have found a dangerous level of resistance and have called for further investigation to take place.

The results were published in the Antimicrobial Agents and Chemotherapy Journal.

"It's remarkable there have been four apparent failures of treatment, there's not been any other published account [in the UK]," Dr. Colin Sutherland, lead scientist from the LSH, told the BBC in a recent interview.

Although the evidence is not yet conclusive, there are signs that the strains are learning to fight back against the drug, which is causing concern.

"It does feel like something is changing, but we're not yet in a crisis. It is an early sign and we need to take it quite seriously as it may be snowballing into something with greater impact," Dr. Sutherland added.

Two out of the four cases in question were picked up while people were visiting Uganda; the other two were infected in Liberia and Angola.

This has caused some worry that there may be resistance to the treatment and that it could be widespread.

Implications

Malaria remains an important public health concern according to the World Health Organization (WHO).

WHO have said that Malaria is a complex illness that varies widely in epidemiology and clinical manifestation in different parts of the world.

These cases in the UK show that strains of malaria, emerging in Africa, can't be cured with most common drugs.

​There is some good news hovewer, as some efforts to fight against the illness, including bed nets, have cut rates of transmission, particularly in Africa, according to the WHO, with the total number of cases in the world dropping by a 21 percent and malaria deaths being cut by half.